The blaze erupted on late Wednesday in the hangar of the Aeroservices company, the Tele Liege broadcaster reported.
Alleged footage from the scene have been shared on social media.
According to the airport's spokesperson, Christian Delcourt, three flights have been redirected to other airports. As all the firefighters were tackling the blaze in the hangar, pilots were allowed to decide whether to land in Liege or not.
The airport later confirmed that no people had been injured as a result of the fire, which, however, caused serious material damage.
Causes of the incident remain unknown.